1. Field of the Invention
The present invention relates to a lithium secondary battery comprising a positive electrode, a non-aqueous electrolyte, and a negative electrode which is an alloy negative electrode and includes a negative electrode current collector having an irregular surface and a negative electrode active material layer formed on the irregular surface.
2. Description of Related Art
A lithium secondary battery that uses as a negative electrode active material aluminum, silicon, or the like electrochemically alloyed with lithium during charge has been proposed in recent years (cf. Japanese Unexamined Patent Publication No. 10-255768). The lithium secondary battery using such an alloy negative electrode, however, has the following problems. Since the negative electrode active material expands and shrinks greatly as a charge-discharge process is repeated, the active material tends to pulverize or peel off from the current collector during charge and discharge. Moreover, wrinkles occur in the current collector during charge and discharge, which degrade the battery's charge-discharge efficiency and cycle performance.
In order to solve the above-noted problems, the present applicant has already proposed a lithium secondary battery that comprises a negative electrode current collector surface formed to have irregularities and an amorphous silicon thin film deposited, as an negative electrode active material layer, on the irregular surface, wherein the surface roughness Ra is restricted to fall within a predetermined range or the tensile strength of the negative electrode current collector is greater than a predetermined value (see Japanese Unexamined Patent Publication Nos. 2002-83594 and 2003-7305).
Nevertheless, even the lithium secondary batteries according to the above-noted publications are in some cases unable to sufficiently prevent the wrinkles in the negative electrode current collector, causing initial charge-discharge characteristics and cycle performance to degrade.